Genetic Divergence and Identification of Two Controversial Lanternfishes (Actinopterygii: Myctophidae: Diaphus) Based on Mitochondrial Cytochrome b Sequences and PCR-RFLP Analysis

Abstract

To resolve the controversial taxonomic status of two closely-related lanternfishes, Diaphus perspicillatus (Ogilby, 1898) and D.gigas Gilbert, 1913, mitochondrial cytochrome b (cyt b) gene sequences of representative individuals were obtained, and specifically-diagnostic restriction sites investigated. In the 5'-half nucleotide sequences of the cyt b gene (594 bp), a relatively high level of nucleotide substitution between the species (8.2-8.7%), together with very low intraspecific variation (<0.86%), was observed, which clearly indicates the two morphs to be specifically distinct. Previous hypotheses regarding gigantism of D.gigas and suspicions regarding the synonymy of the two species are rejected. The nucleotide sequences and practical restriction enzyme assay indicate that any one of four restriction endonucleases (Fok I, Hae III, Nla IV, and Rsa I) can unambiguously discriminate between the two species. Based on specimens identified by molecular analysis, eye diameter and gill raker count were found to be good diagnostic morphological characters.